Ground improvement

As Figure 15.1 shows, there are five execution standards concerned with the execution of ground improvement, as discussed in the following subsections.

15.4.1 Grouting

Figure 15.10 summarizes the scope of EN 12715,17 which deals with the execution of grouting including non-displacement and displacement grouting but excluding jet grouting, which is covered by EN 12716 (see Section 15.4.2). The standard identifies three types of grout (solution, suspension, and mortar) and outlines their characteristics and applicability.

The purpose of grouting is either to reduce the mass permeability (hydraulic conductivity) and/ or to improve the stiffness and density of the ground. This can be achieved by a number of different combinations of grout type, grout design, and injection processes. Emphasis is placed on various properties of grouts, monitoring of their properties and the injection process, and measurement of ground properties before and after grouting.

The importance of an appropriate site investigation is emphasized with checklists of information that an investigation should provide in order to facilitate the grouting operation and, in particular, to enable the design of the grout and injection process. Coupled with an adequate site investigation, EN 12715 emphasizes the need for grouting trials to confirm the design.

Normative references

{definitions]■ j symbols and units ^

—I Definitions and symbols information needed

\ design basis and objectives [ without ground displacement

^_ /permeation (impregnation) grouting

' grouting ^ i-fisiure and contact grouting principles and —i-bulk filling

J P-hydraulic fracturing*

Design considerations j ^-compaction grouting*

"with ground displacement

/type and composition -| grout |—f-parameters and criteria ^applicability

Hdrilling pattern and borehole design grouting sequence grouting pressure —| monitoring and control criteria |

grout I placement

| permeability testing |-f~Site j field grouting trials and grouting tests |— investigation hydraulic binders and cements > clay materials -sands, gravels and fillers -water -

chemical products and admixtures -other materials J

Scope of EN 12715 Execution of special geotechnical work — grouting

1 grout materials

Materials and products suspensions solutions mortars grouts i sampling and testing

"F

-[grout preparation

1 -[grout placement }

^-4 ormitin-o cfwinonr^c storage batching and mixing pumping and delivery j grouting sequences ]•

Execution supervision and control monitoring and control

/environmental impact y control of objective —i-monitoring of displacement f- drilling ^grout

Works documentation

Special [—[ personnel safety \ aspects j—I environmental protection

Figure 15.10. Scope of EN 12715, Execution of... grouting

Non-displacement grouting includes permeation grouting, fissure and contact grouting, and bulk filling, whereas displacement grouting includes hydraulic fracturing and compaction grouting. Although the standard provides a lot of good advice on all aspects of a grouting project, it provides little guidance on the design of the grout mix or details of the method of injection.

EN 12715 was published by CEN in 2000 and re-confirmed for a further five years in 2005.

15.4.2 Jet grouting

Figure 15.11 summarizes the scope of EN 12716,18 which deals with the execution of jet grouting. Jet grouting is considered distinct from grouting because the process aims to disaggregate the soil or weak rock and mix it with the cement agent. It is usual to produce either a column of grouted ground or a panel, vertical or horizontal.

The main structures formed by jet grouting are walls, slabs, canopies, and blocks. These structures may be created using four main processes: single systems (involving disaggregation and cementation carried out by a single fluid); double air systems (involving disaggregation carried out by cement grout supplemented by an air jet shroud); double water systems (involving disaggregation carried out by a high energy water jet with a cement grout used to cement the soil together); and triple systems (involving disaggregation carried out by high energy water jet supplemented by an air jet shroud with a cement grout used to cement the soil together).

Jet grouting can be used to create foundation piles, underpinning, retaining walls, and low permeability barriers.

As with the execution standard for grouting (see Section 15.4.1), EN 12716 does not provide specific design methods but it does provide useful guidance on what needs to be considered for good design and what should be monitored and recorded during construction.

EN 12716 was published by CEN in 2001 and re-confirmed for a further five years in 2006.

I Normative references }

I Terms and definitions

Specific needs J

I Normative references }

{equipment)-preliminary works^j-drilling ( jet grouting}

{placing the reinforcement

{general

/jet grouted column execution method [-jet grouted panel execution method [-alternative execution methods ^ method statement

{equipment)-preliminary works^j-drilling ( jet grouting}

return

{placing the reinforcement

Geotechnical investigation

{Materials

{geometry strength and deformation characteristics y

Scope of EN 12716 Execution of special geotechnical works -jet grouting

-[preliminary tests j

0 0

Post a comment